no xaml was found at the location ‘/mainpage.xaml’

After upgrading a WP7 app to WP8 (VS 2013 RC), I got this very annoying error when trying to run the app in the emulator. “no xaml was found at the location ‘/mainpage.xaml'”.

I came across a conversation on twitter, regarding this, and saw that someone had the same problem, but said “Found it!!! Your application MUST have Invariant Language ticked as a supported language. Blog post to come :-)”

So, that narrowed my search, and I discovered a one line fix; In the AssemblyInfo.cs file, you have to change the line:

[assembly: NeutralResourcesLanguage(“en”, UltimateResourceFallbackLocation.Satellite)]

To

[assembly: NeutralResourcesLanguage(“en”)]

One line fix!. Pity the error message is not helpful at all.